In the following text, reference is made to certain protocols defined by the International Telecommunications Union (ITU), namely:
Protocol nameProtocol DescriptionH.324Terminal for low bit-rate multimedia communicationH.223Multiplexing protocol for low bit rate multimediacommunicationH.245Control protocol for multimedia communicationH.323Packet-based multimedia communications systemsH.248Gateway Control Protocol
There exist many services implemented over circuit switched (CS) access networks with the help of so-called Intelligent Network (IN) nodes. These services are utilized mainly with voice bearers in the CS network. The reason for this is that the devices which are utilized by IN-based services have tended to support only pure voice. There exist however multimedia protocols which are capable of utilizing the CS bearers, e.g ITU-T H.324. Implementations of these protocols can be used for pure video telephony between users which communicate with each other interactively.
A number of deficiencies of existing implementations mean that IN services cannot be used efficiently with H.324 video calls.
Many IN services used for voice calls provide for announcements and prompts to calling subscribers to allow access to and selection of services by means of Dual Tone Multi-Frequency (DTMF) digits. The narrowband multimedia protocol H.324 uses an unrestricted 64 kbit/s digital bearer in 3G-324M applications as seen by the IN-nodes. The content of the 64 kbit/s bearer includes audio, video and control streams multiplexed using the H.223 protocol (Multiplex protocol for low bit rate multimedia communication). The voice announcements played by IN-services are typically stored in PCM coding format. Since the prior art IN-solutions do not include the capability to manipulate the content of unrestricted 64 kbit/s digital calls, IN services do not have the possibility to play announcements for 3G-324M calls.
3G-324M uses efficient audio codecs, e.g. AMR (advanced multi rate) and G.723. These codecs are not capable of transferring the DTMF tones reliably. Thus the DTMF tones are transferred in H.324 by means of control messages, i.e. the H.245 userInputIndication message. Since the prior art IN-solutions do not include the capability to detect the content of unrestricted 64 kbit/s digital calls, IN services do not have the possibility to listen the DTMF tones for 3G-324M calls.